CJ750 toolbox
Another piston meltdown

This one came out of the blue. The oil level was good, the temperature was low, and the bike was loping happily along around 45 mph. The engine suddenly started to behave as if the rotor had come loose or the points were closing up, so I pulled over and took a look under the distributor cap. All was well. Being but a couple miles from home, I decided to nurse the bike back to my garage. Initially, it seemed like everything was going to be fine, and whatever was wrong would be quickly sorted once we were home. However, the engine ran progressively rougher and with progressively less power. It was pretty obvious that something serious was happening, so I stopped and called AAA for a rollback. Once home, I started tearing things apart.
This might explain why the bike was so easy to kick overzero compression on the port jug. The cylinder got damaged too, as did the connecting rod, so this is pretty major. (The starboard side is fine!)
Q: Here's what was in the sump, but it accounts for maybe 20% of the missing piston. Where did the rest of it go?!
A: It was lying on the screen inside the crankcase.
I'm gonna replace the whole motor this time, and thanks to Jimbo, that is indeed on the agenda.

Meanwhile, I'm trying to find the reason this happened. With the previous incident, certain elements were present (straight pipes with undersized jets, running too fast for too long on a hot day, and not recognizing the warning signs.) This time, things were a lot different. I'm running 094 jets with proper fishtails, plenty of fresh SAE40 oil, and most importantly, I was just taking it easy on a nice cool day.

Possibilities? Since this motor is equipped with a deep sump and a high-capacity oil pump with extended pick-up, lubrication has never been a problem. My gut feeling is that the pistons were simply junk.